Comparison between indoor and outdoor air contaminant levels in residential buildings from passive sampler study

The relationships between indoor and outdoor levels of various air contaminants (NO, NO2, SO2 and O3) in 10 non-smoking residential buildings were discussed in this paper. Levels of these four air contaminants from 10 domestic units in Hong Kong were obtained using passive samplers. An integral approach was applied to the mass balance equation and with some approximations, the source and sink strengths of the air contaminants were estimated. It has been found that the average ratios of the indoor and outdoor levels of NO, NO2, SO2 and O3 were 0.98 (S.D.=0.19), 0.79 (S.D.=0.30), 1.01 (S.D.=0.78) and 0.40 (S.D.=0.31), respectively. The results also indicated that the residential buildings in Hong Kong acted as sinks for these four air contaminants on average. The average sink strengths of NO, NO2, SO2 and O3 were 3.01, 0.42, 0.32 and 1.39 mg/h respectively. The deposition velocity of ozone onto wall surfaces in the buildings was estimated to be 0.0225 cm/s. Comparison of the measured data to the newly developed indoor air quality guidance notes in Hong Kong indicated that the nitrogen oxides level needed some concern while the sulphur dioxide and ozone levels were low in the indoor residential environment.